In polluted and moist environments, i.e., in areas with high air humidity, digital contact transducers, used, e.g., in electric power distribution systems, can suffer from low parasitic resistances over open contacts. Such low resistances may result in a false detection of signals originating from contact transducers and may subsequently lead to a false determination of a transducer's state. This, in turn, may cause an unwanted shutdown of at least parts of a power transmission system.
Further, digital input circuits powered by a high-impedance grounded battery may also suffer from a false sensing of digital input signals due to ground faults on the battery feeding lines.
In order to make the sensing of digital input signals more reliable, low-impedance digital inputs with long filter times may be used. However, such inputs suffer from high power losses and slow signal detection. An alternative solution, as disclosed in WO 2008/148793 A1, utilizes the rate of change of the input signal level.